Salt water galvanic cell with steel wool cathode



C. L. OPITZ Sept. 10,1968

v S AL'I WATER GALVANIC CELL WITH STEEL WOOL CATHODE Fi led Aug. 5, 1966 2 Sheets-Sheet 1 NBI FIG. 1

-- CONVERTER INVENTOR. CHARLES L.OPITLZ Agent Sept. 10, 1968 c. L. OPITZ SALT WATER GALVANIC CELL WITH STEEL WOOL CATHODE Filed Aug. 5, 1966 2 Sheets-Sheet 2 2 mm m T .u. m

Y C B United States Patent 3,401,063 SALT WATER GALVANIC CELL WITH STEEL WOOL CATHODE Charles L. Opitz, Westfield, N.J., assignor to Lockheed Aircraft Corporation, Burbank, Calif. Filed Aug. 3, 1966, Ser. No. 569,858 Claims. (Cl. 136100) This invention relates generally to primary cells for the conversion of chemical into electrical energy and more particularly to a galvanic cell for use with salt water electrolytes such as sea water.

The cell employs a porous annular basket containing steel wool or equivalent metal filament type material serving as the cathode. A length of magnesium rod, supported generally concentrically in the annular cavity through the basket, serves as the anode. The use of a steel wool electrode material permits the realization of the very large required cathode area in a compact form. The large area is required to minimize the tendency of a cell to excessively polarize when under load. The ratio of total cathode area to operating current is so selected that the steel wool is provided with cathodic protection against corrosion and yet the current density is not so high as to cause detrimental scaling with magnesium and calcium salts on the cathode. A typical operating current density of 4 milliamperes per square foot of steel cathode area provides this desired condition. The porosity of the steel wool cathode construction permits a continuous diffusion and/or flow of outside sea water into the cell, and this ready supply of fresh electrolyte carries away detrimental waste products and keeps the cell at the desirable low level of polarization.

The term magnesium as used herein is intended to include magnesium alloys in which magnesium is the dominant material. The term steel wool as used herein is intended to include any ferrous material in filament form having physical characteristics as to porosity and surface area of metal per unit volume substantially equivalent to commercial grade steel wool and the term metal wool as used herein is intended to include any metal in the galvanic series of metals which is below (negative in respect to) the magnesium electrode.

A principal object of this invention is to provide an undersea source of electrical power which is relatively independent of pressure (operating depth), temperature and normally encountered variations in salinity.

Another object of this invention is to provide a longlived galvanic cell, utilizing salt water as the electrolyte, capable of output power levels in the .1 watt to watt (continuous operation) range with an operating life for a term of years.

Another object of this invention is to provide a salt water galvanic cell adapted to be immersed in its electrolyte and maintain flow therethrough of the electrolyte for balancing internal and external pressures and maintaining a fresh supply of depolarization electrolyte. Since the cell does not require a fluid-tight enclosure, and is relatively insensitive to pressure, it does not need to be made as heavy and strong as a conventional battery and may be utilized to provide a source of power at virtually any ocean depth.

Another object of this invention is to provide a salt water galvanic cell of the dry charge type having a substantially indefinite shelf life.

Still another object of this invention is to provide an undersea source of electrical power which is economical, both in terms of cost per kilowatt hour and watt hours per pound.

Further and other objects will become apparent from a reading of the following detail description, especially when considered in conjunction with the accompanying drawing, wherein like numerals refer to like parts.

3,401,063 Patented Sept. 10, 1968 In the drawing:

FIGURE 1 is a cutaway, perspective view showing the cell of this invention in a typical power supply system; and

FIGURE 2 is a fragmentary sectional side view of a modified form of cell construction.

Referring to FIGURE 1, the cell includes a porous annular basket 10 constructed of steel webbing 11, or the like, and inner and outer angle rings 12 and 13 at both the top and bottom of the basket to confine the webbing and control the general shape of the basket. The basket should be annular for purposes of carrying out the teachings of this invention, but not necessarily round as shown in the drawing. Also, the webbing 11 may be of a material other than metal.

Basket 10 is fully but loosely packed with metal wool 14 such as steel wool, the preferred material, or its equivalent in filament form. Metal wool 14 serves as the cathode for the galvanic cell and provides a very large surface area relative to the surface area of the anode hereinafter described as is necessary for practical operation of the device.

A generally cylindrically shaped magnesium anode 15 is centrally mounted within opening 16 through the annular basket. A pin 17 projecting from one end of anode 15 is slidably received within a collar 18 secured to a bracket 19 spanning the bottom of basket 10. The other end of anode 15 carries a terminal post pin 20 which projects upwardly through a bracket 21 spanning the top of basket 10. A washer 22 on pin 20 between anode 15 and bracket 21, in combination with spanner bolts 23 and 24 passing through brackets 19 and 21, serves to hold the basket assembly together and the anode in a centered position within the central opening through the basket.

Anode 15 and pin 20 must be electrically insulated from a direct conductive path through the basket to the metal wool cathode 14 and this may be suitably accomplished, for example, by employing a non-conductive material such as a synthetic plastic for pin 17 and washer 22 and by electrically isolating pin 20 from bracket 21 with a sleeve 25 surrounding the pin through an oversized opening 26 in bracket 21. Insulating sleeve 25 may be retained in position by suitable means such as clamp 27.

Terminal post pin 20 is preferably firmly secured to anode 15 such as by threaded engagement 28 so as to minimize electrical resistance between the pin and the anode.

Cathode terminal 29 may be aflixed directly to the metal wool cathode 14 or to an electrically conductive portion of basket 10 which is in electrical contact with the metal cathode material itself. In FIGURE 1, cathode terminal 29 is shown aflixed to the outer bottom ring 30 forming a part of basket 10.

An electrical conductor 31, such as insulated copper wire, is connected to pin 20 serving as the anode terminal and a similar electrical conductor 32 is suitably fastened to cathode terminal 29. The two conductors are coupled across the input of a suitable direct current to direct current, or direct current to alternating current converter 33 such as shown in US. Patents 2,849,615 and 2,987,665. The output from converter 33 is applied across a load 34, it being understood that the load may take the form of any electrically operated device including lights, radio beacons, or other communications equipment.

The cell, when immersed in sea water, will produce useful long-term output voltages in the .35 to .7 volt bracket. The function of converter 33 in the power supply system is to convert the low voltage of the cell into the desired output voltage for a particular load.

A cell of the type and construction above described,

having an outside diameter of 15 inches and a height of 16 inches with a central cylindrical anode of magnesium 6 inches in diameter by 12 inches long and a steel wool cathode material, has recently undergone field testing in a sea water environment. The cell, operating at a cathode current density of 4 milliamps per square foot, produced a nearly constant output voltage averaging .6 volt and a current supply of approximately 275 milliamps for a power output rating of .180 watt on a sustained basis. Over a 194 day operating period, only 3.7 pounds of the 23 pound magnesium anode were consumed. By maintaining the cathode current density at a level which will provide cathodic protection against scaling, the cathode suffers no apparent deterioration throughout the life of the cell, which is limited only by the life of the magnesium anode.

Based on field tests, the estimated ultimate cell life for the test article described above, employing a 23 pound magnesium anode, is approximately 3 /2 years. At a conversion efficiency for magneisum of 226 watt hours per pound, as realized in the field tests, the total energy output capability of the cell is well in excess of 3500 watt hours.

Substantially higher power output than that obtained with the test cell referred to above is obtainable by increasing the size of the unit. A 1500 milliwatt unit has been built (approximately twice the size of the field test unit) and laboratory tested for over a twelve month period, also with excellent results, both in terms of output voltage stability and cell life. These laboratory tests have shown the voltage output of the cell to be substanitally independent of changes in hydrostatic pressure from to 10,000 pounds per square foot. Temperature likewise only moderately affects the terminal voltage of the cell down to the freezing point of sea water, thus qualifying the device for deep sea power supply usage. Since the unit requires no pressure case, no pressure equalizing oil system, nor waterproof enclosure of any kind, it is ideally suited for such environment.

Although a fixed anode cell construction, as shown in FIGURE 1, is capable of generating electrical energy over periods of time measured in terms of years, even longer lived cells may be made using the same concepts with modified structure, as shown in FIGURE 2. Referring to FIGURE 2, there is shown a porous annular basket 40 filled with metal wool 42 and constructed similarly to basket in the FIGURE 1 device. A base 43 for supporting the cell of FIGURE 2 is provided with legs 44 which supportingly engage basket 40 and hold it suspended in a raised position relative to base 43. Brackets 45 secured to the upper portion of basket 40 support a hollow tube 46 above the basket and generally coaxially aligned with annular opening 47 through the basket. Tube 46 is closed at its upper end by an end plate 48. A long magnesium rod 49 is carried within the tube and supported at its lower end 50 on a cone-shaped support member 51 secured to base 43. Support member 51 allows anode 49 to project well into annular opening 47 of basket 40 so that a large surface area of magnesium is available for electro-chemical action with the metal wool cathode in basket 40. Support member 51 is cone-shaped with its apex engaging the anode for two purposes: one, to permit free flow of salt water through the lower portion of the cell and, secondly, to leave substantially the entire end portion of the anode open to the salt water so that, as it is consumed by the electro-chemical action, it will descend into the working area of the cell and supply anode material to the system over an extremely long time period. To maintain anode rod 49 centered in opening 47, a small axial bore 58 may, if desired, be formed in the rod as shown in FIGURE 2, so as to engage the apex of coneshaped support member 51.

With a large portion of the anode being stored in tube 46 and automatically fed to the working area of the cell,

a useful life far in excess of that obtainable with a construction such as shown in FIGURE 1 is possible.

Lower end 52 of tube 46 is flared outwardly over opening 47 in basket 40 such that hydrogen gas evolving from the electro-chemical action between the magnesium anode and metal wool cathode will rise and be trapped inside tube 46 between the wall of the tube and anode rod 49. The buildup of gases in tube 46 will force the salt water out of the tube during operation of the battery, insulating the stored magnesium from salt water deterioration.

Openings 53 and 54 are shown in brackets 44 and 45, respectively, to facilitate the free flow of salt water through the cell while openings 54 serve the additional function of allowing the escape of excess hydrogen gas from the lower end 52 of tube 46. Openings 53 and 54 may obviously be omitted where brackets 44 and 45 are spaced apart sufficiently to permit the necessary free circulation of sea water and an escape route for the excess hydrogen gas.

Magnesium anode rod 49 must be electrically insulated from metal wool cathode 42 in basket 40 and this may be accomplished in various ways such as making tube 46 and support cone 51 from a non-conductive material such as a synthetic plastic. To further ensure insulation of anode 49 from direct electrical contact with the cathode, an insulating ring 57 may be mounted inside opening 47 of basket 40. In this connection, it should be noted the clearance between anode 49 and tube 46 is somewhat exaggerated for clarity in the drawing. While a loose fit is desired to permit automatic gravity feeding of the anode rod into opening 47, a low open space volume in tube 46 is desired to better guide the anode and to permit the cavity to more quickly fill with hydrogen gas for protection of the stored portion of the anode.

The energy output from the cell of FIGURE 2 is ob tained through an anode lead spring 55 connecting with anode 49 through end plate 48 inside tube 46 and a cathode lead 56 suitably coupled to the metal wool cathode 42 such as by embedding a portion of the lead in the metal wool of the cathode. Coupling of the leads to a load may be through a power converter as shown in FIG- URE 1.

Lead spring 55 is coiled Within tube 46 a sufficient number of turns to provide a length of lead permitting feeding of substantially the entire length of anode rod 49 into the working area of the cell. By placing the lead spring in compression, anode 49 may be forceably held on contact with the apex of cone member 51.

The operation of the cell of FIGURE 2 is the same as that described above for FIGURE 1. Since the output voltage of the device is nominally 0.6 volt, it is preferable that converter 33 be located as close to the cell as possible. If load 34 is to be physically located remote from the cell, the long leads should be between the converter and the load rather than between the converter and the cell.

Since the cell is open to the circulation of its sea water environment, no pressure case, no pressure equalizing system, nor a water-proof enclosure of any kind is required. The cell is thus specially suited to deep sea usage. As previously mentioned, the output voltage is substantially independent of temperature and pressure; however, it is necessary for long term operation to maintain the load relatively steady and at a current density factor for the metal wool cathode which will provide cathodic protection. If intermittent heavy loads are required, capacitors or trickle charged low impedance devices would be required in the associated power supplies.

Depolarization of the cell is maintained by the circulation of sea water therethrough, as aided by the selfpumping action of the cell itself.

The two specific embodiments have been shown and described herein for purposes of illustration rather than limitation. While steel wool is considered the preferred cathode material and magnesium the preferred anode material, other combinations of dissimilar metals may be substituted to produce electrical energy at useful voltages and power levels. It is therefore to be understood that certain alterations, modifications and substitutions may be made to the instant disclosure without departing from the spirit and scope of the invention as defined by the appended claims.

I claim:

1. A galvanic cell for generating electrical energy by immersion in a saline water electrolyte comprising, a porous annular basket, a porous metal wool cathode substantially filling said basket except for the center thereof which defines a central cavity, an elongated anode of metal dissimilar to that of the cathode sup ported so as to extend generally concentrically into the central cavity of said annular basket and spaced from said cathode to be electrically insulated from direct physical contact with the basket, and conductor means coupled to said cathode and said anode for obtaining electrical energy from the cell, the cell being so constructed that water contacts the anode through said basket and said porous cathode.

2. A device as defined in claim 1 including a load connecting with said conductor means maintaining a cathode current density providing cathodic protection for the metal wool cathode in the environment of the electrolyte.

3. A device as defined in claim 1 wherein said metal wool is steel wool.

4. A device as defined in claim wherein said anode is magnesium.

5. A device as defined in claim 1 wherein said metal wool is steel wool and said anode is magnesium.

6. A galvanic cell for generating electrical energy by immersion in a saline water electrolyte comprising,

a porous annular basket, a base structure, means secured to said base structure and supporting said basket spaced from the base structure, a metal wool cathode substantially filling said basket except for the center thereof which defines a central cavity, a tube open on one end and closed on the other supported on said basket and disposed over said basket so that its open end faces the base and central cavity through said basket in spaced and generally coaxial relation, an elongated anode of metal dissimilar to that of the cathode projecting into said tube through the central cavity in said basket, a support member secured to said base structure and generally coaxially aligned with said tube and central cavity through said basket for supporting one end of said anode whereby the latter extends substantially through the entire central cavity of said basket, and conductor means coupled to said cathode and said anode for obtaining electrical energy from the cell. 7. A device as defined in claim 6 including compression spring means acting between the closed] end of said tube and said anode forcing the latter into engagement with said support member. 8. A device as defined in claim 6 wherein said support member tapers to a point for supporting contact with said anode. 9. A device as defined in claim 8 including a bore formed axially in said anode and seatingly engaging the point on said support member. 10. A device as defined in claim 6 wherein the open end of said tube is flared over the central cavity in said basket to trap gases released by the electro-chemical action of the cell and protect the portion of the anode projecting inside the tube from the deleterious effects of the electrolyte.

References Cited UNITED STATES PATENTS 793,077 6/1905 Hubbell 13674 1,450,533 4/1923 Williams 13674 1,836,720 12/1931 Martus et a1. 13690 2,234,731 3/1941 Haunz 13674 2,902,530 9/1959 Eisen 136-120 2,977,401 3/1961 Marsal et a1. 136120 3,266,936 8/1966 Krebs 136-74 3,326,724 6/1967 Armitage 13613 FOREIGN PATENTS 4,916 12/1897 Great Britain.

ALLEN B. CURTIS, Primary Examiner.

C. F. LEFEVOUR, Assistant Examiner. 

1. A GALVANIC CELL FOR GENERATING ELECTRICAL ENERGY BY IMMERSION IN A SALINE WATER ELECTROLYTE COMPRISING A POROUS ANNULAR BASKET, A POROUS METAL WOOL CATHODE SUBSTANTIALLY FILLING SAID BASKET EXCEPT FOR THE CENTER THEREOF WHICH DEFINES A CENTRAL CAVITY, AN ELONGATED ANODE OF METAL DISSIMILAR TO THAT OF THE CATHODE SUPPORTED SO AS TO EXTEND GENERALLY CONCENTRICALLY INTO THE CENTRAL CAVITY OF SAID ANNULAR BASKET AND SPACED 